1.Dd April 26 2016 2.Dt NTP_CONF 5 File Formats 3.Os 4.\" EDIT THIS FILE WITH CAUTION (ntp.mdoc) 5.\" 6.\" It has been AutoGen-ed April 26, 2016 at 08:28:36 PM by AutoGen 5.18.5 7.\" From the definitions ntp.conf.def 8.\" and the template file agmdoc-cmd.tpl 9.Sh NAME 10.Nm ntp.conf 11.Nd Network Time Protocol (NTP) daemon configuration file format 12.Sh SYNOPSIS 13.Nm 14.Op Fl \-option\-name 15.Op Fl \-option\-name Ar value 16.Pp 17All arguments must be options. 18.Pp 19.Sh DESCRIPTION 20The 21.Nm 22configuration file is read at initial startup by the 23.Xr ntpd @NTPD_MS@ 24daemon in order to specify the synchronization sources, 25modes and other related information. 26Usually, it is installed in the 27.Pa /etc 28directory, 29but could be installed elsewhere 30(see the daemon's 31.Fl c 32command line option). 33.Pp 34The file format is similar to other 35.Ux 36configuration files. 37Comments begin with a 38.Ql # 39character and extend to the end of the line; 40blank lines are ignored. 41Configuration commands consist of an initial keyword 42followed by a list of arguments, 43some of which may be optional, separated by whitespace. 44Commands may not be continued over multiple lines. 45Arguments may be host names, 46host addresses written in numeric, dotted\-quad form, 47integers, floating point numbers (when specifying times in seconds) 48and text strings. 49.Pp 50The rest of this page describes the configuration and control options. 51The 52.Qq Notes on Configuring NTP and Setting up an NTP Subnet 53page 54(available as part of the HTML documentation 55provided in 56.Pa /usr/share/doc/ntp ) 57contains an extended discussion of these options. 58In addition to the discussion of general 59.Sx Configuration Options , 60there are sections describing the following supported functionality 61and the options used to control it: 62.Bl -bullet -offset indent 63.It 64.Sx Authentication Support 65.It 66.Sx Monitoring Support 67.It 68.Sx Access Control Support 69.It 70.Sx Automatic NTP Configuration Options 71.It 72.Sx Reference Clock Support 73.It 74.Sx Miscellaneous Options 75.El 76.Pp 77Following these is a section describing 78.Sx Miscellaneous Options . 79While there is a rich set of options available, 80the only required option is one or more 81.Ic pool , 82.Ic server , 83.Ic peer , 84.Ic broadcast 85or 86.Ic manycastclient 87commands. 88.Sh Configuration Support 89Following is a description of the configuration commands in 90NTPv4. 91These commands have the same basic functions as in NTPv3 and 92in some cases new functions and new arguments. 93There are two 94classes of commands, configuration commands that configure a 95persistent association with a remote server or peer or reference 96clock, and auxiliary commands that specify environmental variables 97that control various related operations. 98.Ss Configuration Commands 99The various modes are determined by the command keyword and the 100type of the required IP address. 101Addresses are classed by type as 102(s) a remote server or peer (IPv4 class A, B and C), (b) the 103broadcast address of a local interface, (m) a multicast address (IPv4 104class D), or (r) a reference clock address (127.127.x.x). 105Note that 106only those options applicable to each command are listed below. 107Use 108of options not listed may not be caught as an error, but may result 109in some weird and even destructive behavior. 110.Pp 111If the Basic Socket Interface Extensions for IPv6 (RFC\-2553) 112is detected, support for the IPv6 address family is generated 113in addition to the default support of the IPv4 address family. 114In a few cases, including the 115.Cm reslist 116billboard generated 117by 118.Xr ntpq @NTPQ_MS@ 119or 120.Xr ntpdc @NTPDC_MS@ , 121IPv6 addresses are automatically generated. 122IPv6 addresses can be identified by the presence of colons 123.Dq \&: 124in the address field. 125IPv6 addresses can be used almost everywhere where 126IPv4 addresses can be used, 127with the exception of reference clock addresses, 128which are always IPv4. 129.Pp 130Note that in contexts where a host name is expected, a 131.Fl 4 132qualifier preceding 133the host name forces DNS resolution to the IPv4 namespace, 134while a 135.Fl 6 136qualifier forces DNS resolution to the IPv6 namespace. 137See IPv6 references for the 138equivalent classes for that address family. 139.Bl -tag -width indent 140.It Xo Ic pool Ar address 141.Op Cm burst 142.Op Cm iburst 143.Op Cm version Ar version 144.Op Cm prefer 145.Op Cm minpoll Ar minpoll 146.Op Cm maxpoll Ar maxpoll 147.Xc 148.It Xo Ic server Ar address 149.Op Cm key Ar key \&| Cm autokey 150.Op Cm burst 151.Op Cm iburst 152.Op Cm version Ar version 153.Op Cm prefer 154.Op Cm minpoll Ar minpoll 155.Op Cm maxpoll Ar maxpoll 156.Op Cm true 157.Xc 158.It Xo Ic peer Ar address 159.Op Cm key Ar key \&| Cm autokey 160.Op Cm version Ar version 161.Op Cm prefer 162.Op Cm minpoll Ar minpoll 163.Op Cm maxpoll Ar maxpoll 164.Op Cm true 165.Op Cm xleave 166.Xc 167.It Xo Ic broadcast Ar address 168.Op Cm key Ar key \&| Cm autokey 169.Op Cm version Ar version 170.Op Cm prefer 171.Op Cm minpoll Ar minpoll 172.Op Cm ttl Ar ttl 173.Op Cm xleave 174.Xc 175.It Xo Ic manycastclient Ar address 176.Op Cm key Ar key \&| Cm autokey 177.Op Cm version Ar version 178.Op Cm prefer 179.Op Cm minpoll Ar minpoll 180.Op Cm maxpoll Ar maxpoll 181.Op Cm ttl Ar ttl 182.Xc 183.El 184.Pp 185These five commands specify the time server name or address to 186be used and the mode in which to operate. 187The 188.Ar address 189can be 190either a DNS name or an IP address in dotted\-quad notation. 191Additional information on association behavior can be found in the 192.Qq Association Management 193page 194(available as part of the HTML documentation 195provided in 196.Pa /usr/share/doc/ntp ) . 197.Bl -tag -width indent 198.It Ic pool 199For type s addresses, this command mobilizes a persistent 200client mode association with a number of remote servers. 201In this mode the local clock can synchronized to the 202remote server, but the remote server can never be synchronized to 203the local clock. 204.It Ic server 205For type s and r addresses, this command mobilizes a persistent 206client mode association with the specified remote server or local 207radio clock. 208In this mode the local clock can synchronized to the 209remote server, but the remote server can never be synchronized to 210the local clock. 211This command should 212.Em not 213be used for type 214b or m addresses. 215.It Ic peer 216For type s addresses (only), this command mobilizes a 217persistent symmetric\-active mode association with the specified 218remote peer. 219In this mode the local clock can be synchronized to 220the remote peer or the remote peer can be synchronized to the local 221clock. 222This is useful in a network of servers where, depending on 223various failure scenarios, either the local or remote peer may be 224the better source of time. 225This command should NOT be used for type 226b, m or r addresses. 227.It Ic broadcast 228For type b and m addresses (only), this 229command mobilizes a persistent broadcast mode association. 230Multiple 231commands can be used to specify multiple local broadcast interfaces 232(subnets) and/or multiple multicast groups. 233Note that local 234broadcast messages go only to the interface associated with the 235subnet specified, but multicast messages go to all interfaces. 236In broadcast mode the local server sends periodic broadcast 237messages to a client population at the 238.Ar address 239specified, which is usually the broadcast address on (one of) the 240local network(s) or a multicast address assigned to NTP. 241The IANA 242has assigned the multicast group address IPv4 224.0.1.1 and 243IPv6 ff05::101 (site local) exclusively to 244NTP, but other nonconflicting addresses can be used to contain the 245messages within administrative boundaries. 246Ordinarily, this 247specification applies only to the local server operating as a 248sender; for operation as a broadcast client, see the 249.Ic broadcastclient 250or 251.Ic multicastclient 252commands 253below. 254.It Ic manycastclient 255For type m addresses (only), this command mobilizes a 256manycast client mode association for the multicast address 257specified. 258In this case a specific address must be supplied which 259matches the address used on the 260.Ic manycastserver 261command for 262the designated manycast servers. 263The NTP multicast address 264224.0.1.1 assigned by the IANA should NOT be used, unless specific 265means are taken to avoid spraying large areas of the Internet with 266these messages and causing a possibly massive implosion of replies 267at the sender. 268The 269.Ic manycastserver 270command specifies that the local server 271is to operate in client mode with the remote servers that are 272discovered as the result of broadcast/multicast messages. 273The 274client broadcasts a request message to the group address associated 275with the specified 276.Ar address 277and specifically enabled 278servers respond to these messages. 279The client selects the servers 280providing the best time and continues as with the 281.Ic server 282command. 283The remaining servers are discarded as if never 284heard. 285.El 286.Pp 287Options: 288.Bl -tag -width indent 289.It Cm autokey 290All packets sent to and received from the server or peer are to 291include authentication fields encrypted using the autokey scheme 292described in 293.Sx Authentication Options . 294.It Cm burst 295when the server is reachable, send a burst of eight packets 296instead of the usual one. 297The packet spacing is normally 2 s; 298however, the spacing between the first and second packets 299can be changed with the 300.Ic calldelay 301command to allow 302additional time for a modem or ISDN call to complete. 303This is designed to improve timekeeping quality 304with the 305.Ic server 306command and s addresses. 307.It Cm iburst 308When the server is unreachable, send a burst of eight packets 309instead of the usual one. 310The packet spacing is normally 2 s; 311however, the spacing between the first two packets can be 312changed with the 313.Ic calldelay 314command to allow 315additional time for a modem or ISDN call to complete. 316This is designed to speed the initial synchronization 317acquisition with the 318.Ic server 319command and s addresses and when 320.Xr ntpd @NTPD_MS@ 321is started with the 322.Fl q 323option. 324.It Cm key Ar key 325All packets sent to and received from the server or peer are to 326include authentication fields encrypted using the specified 327.Ar key 328identifier with values from 1 to 65534, inclusive. 329The 330default is to include no encryption field. 331.It Cm minpoll Ar minpoll 332.It Cm maxpoll Ar maxpoll 333These options specify the minimum and maximum poll intervals 334for NTP messages, as a power of 2 in seconds 335The maximum poll 336interval defaults to 10 (1,024 s), but can be increased by the 337.Cm maxpoll 338option to an upper limit of 17 (36.4 h). 339The 340minimum poll interval defaults to 6 (64 s), but can be decreased by 341the 342.Cm minpoll 343option to a lower limit of 4 (16 s). 344.It Cm noselect 345Marks the server as unused, except for display purposes. 346The server is discarded by the selection algroithm. 347.It Cm preempt 348Says the association can be preempted. 349.It Cm true 350Marks the server as a truechimer. 351Use this option only for testing. 352.It Cm prefer 353Marks the server as preferred. 354All other things being equal, 355this host will be chosen for synchronization among a set of 356correctly operating hosts. 357See the 358.Qq Mitigation Rules and the prefer Keyword 359page 360(available as part of the HTML documentation 361provided in 362.Pa /usr/share/doc/ntp ) 363for further information. 364.It Cm true 365Forces the association to always survive the selection and clustering algorithms. 366This option should almost certainly 367.Em only 368be used while testing an association. 369.It Cm ttl Ar ttl 370This option is used only with broadcast server and manycast 371client modes. 372It specifies the time\-to\-live 373.Ar ttl 374to 375use on broadcast server and multicast server and the maximum 376.Ar ttl 377for the expanding ring search with manycast 378client packets. 379Selection of the proper value, which defaults to 380127, is something of a black art and should be coordinated with the 381network administrator. 382.It Cm version Ar version 383Specifies the version number to be used for outgoing NTP 384packets. 385Versions 1\-4 are the choices, with version 4 the 386default. 387.It Cm xleave 388Valid in 389.Cm peer 390and 391.Cm broadcast 392modes only, this flag enables interleave mode. 393.El 394.Ss Auxiliary Commands 395.Bl -tag -width indent 396.It Ic broadcastclient 397This command enables reception of broadcast server messages to 398any local interface (type b) address. 399Upon receiving a message for 400the first time, the broadcast client measures the nominal server 401propagation delay using a brief client/server exchange with the 402server, then enters the broadcast client mode, in which it 403synchronizes to succeeding broadcast messages. 404Note that, in order 405to avoid accidental or malicious disruption in this mode, both the 406server and client should operate using symmetric\-key or public\-key 407authentication as described in 408.Sx Authentication Options . 409.It Ic manycastserver Ar address ... 410This command enables reception of manycast client messages to 411the multicast group address(es) (type m) specified. 412At least one 413address is required, but the NTP multicast address 224.0.1.1 414assigned by the IANA should NOT be used, unless specific means are 415taken to limit the span of the reply and avoid a possibly massive 416implosion at the original sender. 417Note that, in order to avoid 418accidental or malicious disruption in this mode, both the server 419and client should operate using symmetric\-key or public\-key 420authentication as described in 421.Sx Authentication Options . 422.It Ic multicastclient Ar address ... 423This command enables reception of multicast server messages to 424the multicast group address(es) (type m) specified. 425Upon receiving 426a message for the first time, the multicast client measures the 427nominal server propagation delay using a brief client/server 428exchange with the server, then enters the broadcast client mode, in 429which it synchronizes to succeeding multicast messages. 430Note that, 431in order to avoid accidental or malicious disruption in this mode, 432both the server and client should operate using symmetric\-key or 433public\-key authentication as described in 434.Sx Authentication Options . 435.It Ic mdnstries Ar number 436If we are participating in mDNS, 437after we have synched for the first time 438we attempt to register with the mDNS system. 439If that registration attempt fails, 440we try again at one minute intervals for up to 441.Ic mdnstries 442times. 443After all, 444.Ic ntpd 445may be starting before mDNS. 446The default value for 447.Ic mdnstries 448is 5. 449.El 450.Sh Authentication Support 451Authentication support allows the NTP client to verify that the 452server is in fact known and trusted and not an intruder intending 453accidentally or on purpose to masquerade as that server. 454The NTPv3 455specification RFC\-1305 defines a scheme which provides 456cryptographic authentication of received NTP packets. 457Originally, 458this was done using the Data Encryption Standard (DES) algorithm 459operating in Cipher Block Chaining (CBC) mode, commonly called 460DES\-CBC. 461Subsequently, this was replaced by the RSA Message Digest 4625 (MD5) algorithm using a private key, commonly called keyed\-MD5. 463Either algorithm computes a message digest, or one\-way hash, which 464can be used to verify the server has the correct private key and 465key identifier. 466.Pp 467NTPv4 retains the NTPv3 scheme, properly described as symmetric key 468cryptography and, in addition, provides a new Autokey scheme 469based on public key cryptography. 470Public key cryptography is generally considered more secure 471than symmetric key cryptography, since the security is based 472on a private value which is generated by each server and 473never revealed. 474With Autokey all key distribution and 475management functions involve only public values, which 476considerably simplifies key distribution and storage. 477Public key management is based on X.509 certificates, 478which can be provided by commercial services or 479produced by utility programs in the OpenSSL software library 480or the NTPv4 distribution. 481.Pp 482While the algorithms for symmetric key cryptography are 483included in the NTPv4 distribution, public key cryptography 484requires the OpenSSL software library to be installed 485before building the NTP distribution. 486Directions for doing that 487are on the Building and Installing the Distribution page. 488.Pp 489Authentication is configured separately for each association 490using the 491.Cm key 492or 493.Cm autokey 494subcommand on the 495.Ic peer , 496.Ic server , 497.Ic broadcast 498and 499.Ic manycastclient 500configuration commands as described in 501.Sx Configuration Options 502page. 503The authentication 504options described below specify the locations of the key files, 505if other than default, which symmetric keys are trusted 506and the interval between various operations, if other than default. 507.Pp 508Authentication is always enabled, 509although ineffective if not configured as 510described below. 511If a NTP packet arrives 512including a message authentication 513code (MAC), it is accepted only if it 514passes all cryptographic checks. 515The 516checks require correct key ID, key value 517and message digest. 518If the packet has 519been modified in any way or replayed 520by an intruder, it will fail one or more 521of these checks and be discarded. 522Furthermore, the Autokey scheme requires a 523preliminary protocol exchange to obtain 524the server certificate, verify its 525credentials and initialize the protocol 526.Pp 527The 528.Cm auth 529flag controls whether new associations or 530remote configuration commands require cryptographic authentication. 531This flag can be set or reset by the 532.Ic enable 533and 534.Ic disable 535commands and also by remote 536configuration commands sent by a 537.Xr ntpdc @NTPDC_MS@ 538program running on 539another machine. 540If this flag is enabled, which is the default 541case, new broadcast client and symmetric passive associations and 542remote configuration commands must be cryptographically 543authenticated using either symmetric key or public key cryptography. 544If this 545flag is disabled, these operations are effective 546even if not cryptographic 547authenticated. 548It should be understood 549that operating with the 550.Ic auth 551flag disabled invites a significant vulnerability 552where a rogue hacker can 553masquerade as a falseticker and seriously 554disrupt system timekeeping. 555It is 556important to note that this flag has no purpose 557other than to allow or disallow 558a new association in response to new broadcast 559and symmetric active messages 560and remote configuration commands and, in particular, 561the flag has no effect on 562the authentication process itself. 563.Pp 564An attractive alternative where multicast support is available 565is manycast mode, in which clients periodically troll 566for servers as described in the 567.Sx Automatic NTP Configuration Options 568page. 569Either symmetric key or public key 570cryptographic authentication can be used in this mode. 571The principle advantage 572of manycast mode is that potential servers need not be 573configured in advance, 574since the client finds them during regular operation, 575and the configuration 576files for all clients can be identical. 577.Pp 578The security model and protocol schemes for 579both symmetric key and public key 580cryptography are summarized below; 581further details are in the briefings, papers 582and reports at the NTP project page linked from 583.Li http://www.ntp.org/ . 584.Ss Symmetric\-Key Cryptography 585The original RFC\-1305 specification allows any one of possibly 58665,534 keys, each distinguished by a 32\-bit key identifier, to 587authenticate an association. 588The servers and clients involved must 589agree on the key and key identifier to 590authenticate NTP packets. 591Keys and 592related information are specified in a key 593file, usually called 594.Pa ntp.keys , 595which must be distributed and stored using 596secure means beyond the scope of the NTP protocol itself. 597Besides the keys used 598for ordinary NTP associations, 599additional keys can be used as passwords for the 600.Xr ntpq @NTPQ_MS@ 601and 602.Xr ntpdc @NTPDC_MS@ 603utility programs. 604.Pp 605When 606.Xr ntpd @NTPD_MS@ 607is first started, it reads the key file specified in the 608.Ic keys 609configuration command and installs the keys 610in the key cache. 611However, 612individual keys must be activated with the 613.Ic trusted 614command before use. 615This 616allows, for instance, the installation of possibly 617several batches of keys and 618then activating or deactivating each batch 619remotely using 620.Xr ntpdc @NTPDC_MS@ . 621This also provides a revocation capability that can be used 622if a key becomes compromised. 623The 624.Ic requestkey 625command selects the key used as the password for the 626.Xr ntpdc @NTPDC_MS@ 627utility, while the 628.Ic controlkey 629command selects the key used as the password for the 630.Xr ntpq @NTPQ_MS@ 631utility. 632.Ss Public Key Cryptography 633NTPv4 supports the original NTPv3 symmetric key scheme 634described in RFC\-1305 and in addition the Autokey protocol, 635which is based on public key cryptography. 636The Autokey Version 2 protocol described on the Autokey Protocol 637page verifies packet integrity using MD5 message digests 638and verifies the source with digital signatures and any of several 639digest/signature schemes. 640Optional identity schemes described on the Identity Schemes 641page and based on cryptographic challenge/response algorithms 642are also available. 643Using all of these schemes provides strong security against 644replay with or without modification, spoofing, masquerade 645and most forms of clogging attacks. 646.\" .Pp 647.\" The cryptographic means necessary for all Autokey operations 648.\" is provided by the OpenSSL software library. 649.\" This library is available from http://www.openssl.org/ 650.\" and can be installed using the procedures outlined 651.\" in the Building and Installing the Distribution page. 652.\" Once installed, 653.\" the configure and build 654.\" process automatically detects the library and links 655.\" the library routines required. 656.Pp 657The Autokey protocol has several modes of operation 658corresponding to the various NTP modes supported. 659Most modes use a special cookie which can be 660computed independently by the client and server, 661but encrypted in transmission. 662All modes use in addition a variant of the S\-KEY scheme, 663in which a pseudo\-random key list is generated and used 664in reverse order. 665These schemes are described along with an executive summary, 666current status, briefing slides and reading list on the 667.Sx Autonomous Authentication 668page. 669.Pp 670The specific cryptographic environment used by Autokey servers 671and clients is determined by a set of files 672and soft links generated by the 673.Xr ntp\-keygen 1ntpkeygenmdoc 674program. 675This includes a required host key file, 676required certificate file and optional sign key file, 677leapsecond file and identity scheme files. 678The 679digest/signature scheme is specified in the X.509 certificate 680along with the matching sign key. 681There are several schemes 682available in the OpenSSL software library, each identified 683by a specific string such as 684.Cm md5WithRSAEncryption , 685which stands for the MD5 message digest with RSA 686encryption scheme. 687The current NTP distribution supports 688all the schemes in the OpenSSL library, including 689those based on RSA and DSA digital signatures. 690.Pp 691NTP secure groups can be used to define cryptographic compartments 692and security hierarchies. 693It is important that every host 694in the group be able to construct a certificate trail to one 695or more trusted hosts in the same group. 696Each group 697host runs the Autokey protocol to obtain the certificates 698for all hosts along the trail to one or more trusted hosts. 699This requires the configuration file in all hosts to be 700engineered so that, even under anticipated failure conditions, 701the NTP subnet will form such that every group host can find 702a trail to at least one trusted host. 703.Ss Naming and Addressing 704It is important to note that Autokey does not use DNS to 705resolve addresses, since DNS can't be completely trusted 706until the name servers have synchronized clocks. 707The cryptographic name used by Autokey to bind the host identity 708credentials and cryptographic values must be independent 709of interface, network and any other naming convention. 710The name appears in the host certificate in either or both 711the subject and issuer fields, so protection against 712DNS compromise is essential. 713.Pp 714By convention, the name of an Autokey host is the name returned 715by the Unix 716.Xr gethostname 2 717system call or equivalent in other systems. 718By the system design 719model, there are no provisions to allow alternate names or aliases. 720However, this is not to say that DNS aliases, different names 721for each interface, etc., are constrained in any way. 722.Pp 723It is also important to note that Autokey verifies authenticity 724using the host name, network address and public keys, 725all of which are bound together by the protocol specifically 726to deflect masquerade attacks. 727For this reason Autokey 728includes the source and destination IP addresses in message digest 729computations and so the same addresses must be available 730at both the server and client. 731For this reason operation 732with network address translation schemes is not possible. 733This reflects the intended robust security model where government 734and corporate NTP servers are operated outside firewall perimeters. 735.Ss Operation 736A specific combination of authentication scheme (none, 737symmetric key, public key) and identity scheme is called 738a cryptotype, although not all combinations are compatible. 739There may be management configurations where the clients, 740servers and peers may not all support the same cryptotypes. 741A secure NTPv4 subnet can be configured in many ways while 742keeping in mind the principles explained above and 743in this section. 744Note however that some cryptotype 745combinations may successfully interoperate with each other, 746but may not represent good security practice. 747.Pp 748The cryptotype of an association is determined at the time 749of mobilization, either at configuration time or some time 750later when a message of appropriate cryptotype arrives. 751When mobilized by a 752.Ic server 753or 754.Ic peer 755configuration command and no 756.Ic key 757or 758.Ic autokey 759subcommands are present, the association is not 760authenticated; if the 761.Ic key 762subcommand is present, the association is authenticated 763using the symmetric key ID specified; if the 764.Ic autokey 765subcommand is present, the association is authenticated 766using Autokey. 767.Pp 768When multiple identity schemes are supported in the Autokey 769protocol, the first message exchange determines which one is used. 770The client request message contains bits corresponding 771to which schemes it has available. 772The server response message 773contains bits corresponding to which schemes it has available. 774Both server and client match the received bits with their own 775and select a common scheme. 776.Pp 777Following the principle that time is a public value, 778a server responds to any client packet that matches 779its cryptotype capabilities. 780Thus, a server receiving 781an unauthenticated packet will respond with an unauthenticated 782packet, while the same server receiving a packet of a cryptotype 783it supports will respond with packets of that cryptotype. 784However, unconfigured broadcast or manycast client 785associations or symmetric passive associations will not be 786mobilized unless the server supports a cryptotype compatible 787with the first packet received. 788By default, unauthenticated associations will not be mobilized 789unless overridden in a decidedly dangerous way. 790.Pp 791Some examples may help to reduce confusion. 792Client Alice has no specific cryptotype selected. 793Server Bob has both a symmetric key file and minimal Autokey files. 794Alice's unauthenticated messages arrive at Bob, who replies with 795unauthenticated messages. 796Cathy has a copy of Bob's symmetric 797key file and has selected key ID 4 in messages to Bob. 798Bob verifies the message with his key ID 4. 799If it's the 800same key and the message is verified, Bob sends Cathy a reply 801authenticated with that key. 802If verification fails, 803Bob sends Cathy a thing called a crypto\-NAK, which tells her 804something broke. 805She can see the evidence using the 806.Xr ntpq @NTPQ_MS@ 807program. 808.Pp 809Denise has rolled her own host key and certificate. 810She also uses one of the identity schemes as Bob. 811She sends the first Autokey message to Bob and they 812both dance the protocol authentication and identity steps. 813If all comes out okay, Denise and Bob continue as described above. 814.Pp 815It should be clear from the above that Bob can support 816all the girls at the same time, as long as he has compatible 817authentication and identity credentials. 818Now, Bob can act just like the girls in his own choice of servers; 819he can run multiple configured associations with multiple different 820servers (or the same server, although that might not be useful). 821But, wise security policy might preclude some cryptotype 822combinations; for instance, running an identity scheme 823with one server and no authentication with another might not be wise. 824.Ss Key Management 825The cryptographic values used by the Autokey protocol are 826incorporated as a set of files generated by the 827.Xr ntp\-keygen 1ntpkeygenmdoc 828utility program, including symmetric key, host key and 829public certificate files, as well as sign key, identity parameters 830and leapseconds files. 831Alternatively, host and sign keys and 832certificate files can be generated by the OpenSSL utilities 833and certificates can be imported from public certificate 834authorities. 835Note that symmetric keys are necessary for the 836.Xr ntpq @NTPQ_MS@ 837and 838.Xr ntpdc @NTPDC_MS@ 839utility programs. 840The remaining files are necessary only for the 841Autokey protocol. 842.Pp 843Certificates imported from OpenSSL or public certificate 844authorities have certian limitations. 845The certificate should be in ASN.1 syntax, X.509 Version 3 846format and encoded in PEM, which is the same format 847used by OpenSSL. 848The overall length of the certificate encoded 849in ASN.1 must not exceed 1024 bytes. 850The subject distinguished 851name field (CN) is the fully qualified name of the host 852on which it is used; the remaining subject fields are ignored. 853The certificate extension fields must not contain either 854a subject key identifier or a issuer key identifier field; 855however, an extended key usage field for a trusted host must 856contain the value 857.Cm trustRoot ; . 858Other extension fields are ignored. 859.Ss Authentication Commands 860.Bl -tag -width indent 861.It Ic autokey Op Ar logsec 862Specifies the interval between regenerations of the session key 863list used with the Autokey protocol. 864Note that the size of the key 865list for each association depends on this interval and the current 866poll interval. 867The default value is 12 (4096 s or about 1.1 hours). 868For poll intervals above the specified interval, a session key list 869with a single entry will be regenerated for every message 870sent. 871.It Ic controlkey Ar key 872Specifies the key identifier to use with the 873.Xr ntpq @NTPQ_MS@ 874utility, which uses the standard 875protocol defined in RFC\-1305. 876The 877.Ar key 878argument is 879the key identifier for a trusted key, where the value can be in the 880range 1 to 65,534, inclusive. 881.It Xo Ic crypto 882.Op Cm cert Ar file 883.Op Cm leap Ar file 884.Op Cm randfile Ar file 885.Op Cm host Ar file 886.Op Cm sign Ar file 887.Op Cm gq Ar file 888.Op Cm gqpar Ar file 889.Op Cm iffpar Ar file 890.Op Cm mvpar Ar file 891.Op Cm pw Ar password 892.Xc 893This command requires the OpenSSL library. 894It activates public key 895cryptography, selects the message digest and signature 896encryption scheme and loads the required private and public 897values described above. 898If one or more files are left unspecified, 899the default names are used as described above. 900Unless the complete path and name of the file are specified, the 901location of a file is relative to the keys directory specified 902in the 903.Ic keysdir 904command or default 905.Pa /usr/local/etc . 906Following are the subcommands: 907.Bl -tag -width indent 908.It Cm cert Ar file 909Specifies the location of the required host public certificate file. 910This overrides the link 911.Pa ntpkey_cert_ Ns Ar hostname 912in the keys directory. 913.It Cm gqpar Ar file 914Specifies the location of the optional GQ parameters file. 915This 916overrides the link 917.Pa ntpkey_gq_ Ns Ar hostname 918in the keys directory. 919.It Cm host Ar file 920Specifies the location of the required host key file. 921This overrides 922the link 923.Pa ntpkey_key_ Ns Ar hostname 924in the keys directory. 925.It Cm iffpar Ar file 926Specifies the location of the optional IFF parameters file. 927This overrides the link 928.Pa ntpkey_iff_ Ns Ar hostname 929in the keys directory. 930.It Cm leap Ar file 931Specifies the location of the optional leapsecond file. 932This overrides the link 933.Pa ntpkey_leap 934in the keys directory. 935.It Cm mvpar Ar file 936Specifies the location of the optional MV parameters file. 937This overrides the link 938.Pa ntpkey_mv_ Ns Ar hostname 939in the keys directory. 940.It Cm pw Ar password 941Specifies the password to decrypt files containing private keys and 942identity parameters. 943This is required only if these files have been 944encrypted. 945.It Cm randfile Ar file 946Specifies the location of the random seed file used by the OpenSSL 947library. 948The defaults are described in the main text above. 949.It Cm sign Ar file 950Specifies the location of the optional sign key file. 951This overrides 952the link 953.Pa ntpkey_sign_ Ns Ar hostname 954in the keys directory. 955If this file is 956not found, the host key is also the sign key. 957.El 958.It Ic keys Ar keyfile 959Specifies the complete path and location of the MD5 key file 960containing the keys and key identifiers used by 961.Xr ntpd @NTPD_MS@ , 962.Xr ntpq @NTPQ_MS@ 963and 964.Xr ntpdc @NTPDC_MS@ 965when operating with symmetric key cryptography. 966This is the same operation as the 967.Fl k 968command line option. 969.It Ic keysdir Ar path 970This command specifies the default directory path for 971cryptographic keys, parameters and certificates. 972The default is 973.Pa /usr/local/etc/ . 974.It Ic requestkey Ar key 975Specifies the key identifier to use with the 976.Xr ntpdc @NTPDC_MS@ 977utility program, which uses a 978proprietary protocol specific to this implementation of 979.Xr ntpd @NTPD_MS@ . 980The 981.Ar key 982argument is a key identifier 983for the trusted key, where the value can be in the range 1 to 98465,534, inclusive. 985.It Ic revoke Ar logsec 986Specifies the interval between re\-randomization of certain 987cryptographic values used by the Autokey scheme, as a power of 2 in 988seconds. 989These values need to be updated frequently in order to 990deflect brute\-force attacks on the algorithms of the scheme; 991however, updating some values is a relatively expensive operation. 992The default interval is 16 (65,536 s or about 18 hours). 993For poll 994intervals above the specified interval, the values will be updated 995for every message sent. 996.It Ic trustedkey Ar key ... 997Specifies the key identifiers which are trusted for the 998purposes of authenticating peers with symmetric key cryptography, 999as well as keys used by the 1000.Xr ntpq @NTPQ_MS@ 1001and 1002.Xr ntpdc @NTPDC_MS@ 1003programs. 1004The authentication procedures require that both the local 1005and remote servers share the same key and key identifier for this 1006purpose, although different keys can be used with different 1007servers. 1008The 1009.Ar key 1010arguments are 32\-bit unsigned 1011integers with values from 1 to 65,534. 1012.El 1013.Ss Error Codes 1014The following error codes are reported via the NTP control 1015and monitoring protocol trap mechanism. 1016.Bl -tag -width indent 1017.It 101 1018.Pq bad field format or length 1019The packet has invalid version, length or format. 1020.It 102 1021.Pq bad timestamp 1022The packet timestamp is the same or older than the most recent received. 1023This could be due to a replay or a server clock time step. 1024.It 103 1025.Pq bad filestamp 1026The packet filestamp is the same or older than the most recent received. 1027This could be due to a replay or a key file generation error. 1028.It 104 1029.Pq bad or missing public key 1030The public key is missing, has incorrect format or is an unsupported type. 1031.It 105 1032.Pq unsupported digest type 1033The server requires an unsupported digest/signature scheme. 1034.It 106 1035.Pq mismatched digest types 1036Not used. 1037.It 107 1038.Pq bad signature length 1039The signature length does not match the current public key. 1040.It 108 1041.Pq signature not verified 1042The message fails the signature check. 1043It could be bogus or signed by a 1044different private key. 1045.It 109 1046.Pq certificate not verified 1047The certificate is invalid or signed with the wrong key. 1048.It 110 1049.Pq certificate not verified 1050The certificate is not yet valid or has expired or the signature could not 1051be verified. 1052.It 111 1053.Pq bad or missing cookie 1054The cookie is missing, corrupted or bogus. 1055.It 112 1056.Pq bad or missing leapseconds table 1057The leapseconds table is missing, corrupted or bogus. 1058.It 113 1059.Pq bad or missing certificate 1060The certificate is missing, corrupted or bogus. 1061.It 114 1062.Pq bad or missing identity 1063The identity key is missing, corrupt or bogus. 1064.El 1065.Sh Monitoring Support 1066.Xr ntpd @NTPD_MS@ 1067includes a comprehensive monitoring facility suitable 1068for continuous, long term recording of server and client 1069timekeeping performance. 1070See the 1071.Ic statistics 1072command below 1073for a listing and example of each type of statistics currently 1074supported. 1075Statistic files are managed using file generation sets 1076and scripts in the 1077.Pa ./scripts 1078directory of the source code distribution. 1079Using 1080these facilities and 1081.Ux 1082.Xr cron 8 1083jobs, the data can be 1084automatically summarized and archived for retrospective analysis. 1085.Ss Monitoring Commands 1086.Bl -tag -width indent 1087.It Ic statistics Ar name ... 1088Enables writing of statistics records. 1089Currently, eight kinds of 1090.Ar name 1091statistics are supported. 1092.Bl -tag -width indent 1093.It Cm clockstats 1094Enables recording of clock driver statistics information. 1095Each update 1096received from a clock driver appends a line of the following form to 1097the file generation set named 1098.Cm clockstats : 1099.Bd -literal 110049213 525.624 127.127.4.1 93 226 00:08:29.606 D 1101.Ed 1102.Pp 1103The first two fields show the date (Modified Julian Day) and time 1104(seconds and fraction past UTC midnight). 1105The next field shows the 1106clock address in dotted\-quad notation. 1107The final field shows the last 1108timecode received from the clock in decoded ASCII format, where 1109meaningful. 1110In some clock drivers a good deal of additional information 1111can be gathered and displayed as well. 1112See information specific to each 1113clock for further details. 1114.It Cm cryptostats 1115This option requires the OpenSSL cryptographic software library. 1116It 1117enables recording of cryptographic public key protocol information. 1118Each message received by the protocol module appends a line of the 1119following form to the file generation set named 1120.Cm cryptostats : 1121.Bd -literal 112249213 525.624 127.127.4.1 message 1123.Ed 1124.Pp 1125The first two fields show the date (Modified Julian Day) and time 1126(seconds and fraction past UTC midnight). 1127The next field shows the peer 1128address in dotted\-quad notation, The final message field includes the 1129message type and certain ancillary information. 1130See the 1131.Sx Authentication Options 1132section for further information. 1133.It Cm loopstats 1134Enables recording of loop filter statistics information. 1135Each 1136update of the local clock outputs a line of the following form to 1137the file generation set named 1138.Cm loopstats : 1139.Bd -literal 114050935 75440.031 0.000006019 13.778190 0.000351733 0.0133806 1141.Ed 1142.Pp 1143The first two fields show the date (Modified Julian Day) and 1144time (seconds and fraction past UTC midnight). 1145The next five fields 1146show time offset (seconds), frequency offset (parts per million \- 1147PPM), RMS jitter (seconds), Allan deviation (PPM) and clock 1148discipline time constant. 1149.It Cm peerstats 1150Enables recording of peer statistics information. 1151This includes 1152statistics records of all peers of a NTP server and of special 1153signals, where present and configured. 1154Each valid update appends a 1155line of the following form to the current element of a file 1156generation set named 1157.Cm peerstats : 1158.Bd -literal 115948773 10847.650 127.127.4.1 9714 \-0.001605376 0.000000000 0.001424877 0.000958674 1160.Ed 1161.Pp 1162The first two fields show the date (Modified Julian Day) and 1163time (seconds and fraction past UTC midnight). 1164The next two fields 1165show the peer address in dotted\-quad notation and status, 1166respectively. 1167The status field is encoded in hex in the format 1168described in Appendix A of the NTP specification RFC 1305. 1169The final four fields show the offset, 1170delay, dispersion and RMS jitter, all in seconds. 1171.It Cm rawstats 1172Enables recording of raw\-timestamp statistics information. 1173This 1174includes statistics records of all peers of a NTP server and of 1175special signals, where present and configured. 1176Each NTP message 1177received from a peer or clock driver appends a line of the 1178following form to the file generation set named 1179.Cm rawstats : 1180.Bd -literal 118150928 2132.543 128.4.1.1 128.4.1.20 3102453281.584327000 3102453281.58622800031 02453332.540806000 3102453332.541458000 1182.Ed 1183.Pp 1184The first two fields show the date (Modified Julian Day) and 1185time (seconds and fraction past UTC midnight). 1186The next two fields 1187show the remote peer or clock address followed by the local address 1188in dotted\-quad notation. 1189The final four fields show the originate, 1190receive, transmit and final NTP timestamps in order. 1191The timestamp 1192values are as received and before processing by the various data 1193smoothing and mitigation algorithms. 1194.It Cm sysstats 1195Enables recording of ntpd statistics counters on a periodic basis. 1196Each 1197hour a line of the following form is appended to the file generation 1198set named 1199.Cm sysstats : 1200.Bd -literal 120150928 2132.543 36000 81965 0 9546 56 71793 512 540 10 147 1202.Ed 1203.Pp 1204The first two fields show the date (Modified Julian Day) and time 1205(seconds and fraction past UTC midnight). 1206The remaining ten fields show 1207the statistics counter values accumulated since the last generated 1208line. 1209.Bl -tag -width indent 1210.It Time since restart Cm 36000 1211Time in hours since the system was last rebooted. 1212.It Packets received Cm 81965 1213Total number of packets received. 1214.It Packets processed Cm 0 1215Number of packets received in response to previous packets sent 1216.It Current version Cm 9546 1217Number of packets matching the current NTP version. 1218.It Previous version Cm 56 1219Number of packets matching the previous NTP version. 1220.It Bad version Cm 71793 1221Number of packets matching neither NTP version. 1222.It Access denied Cm 512 1223Number of packets denied access for any reason. 1224.It Bad length or format Cm 540 1225Number of packets with invalid length, format or port number. 1226.It Bad authentication Cm 10 1227Number of packets not verified as authentic. 1228.It Rate exceeded Cm 147 1229Number of packets discarded due to rate limitation. 1230.El 1231.It Cm statsdir Ar directory_path 1232Indicates the full path of a directory where statistics files 1233should be created (see below). 1234This keyword allows 1235the (otherwise constant) 1236.Cm filegen 1237filename prefix to be modified for file generation sets, which 1238is useful for handling statistics logs. 1239.It Cm filegen Ar name Xo 1240.Op Cm file Ar filename 1241.Op Cm type Ar typename 1242.Op Cm link | nolink 1243.Op Cm enable | disable 1244.Xc 1245Configures setting of generation file set name. 1246Generation 1247file sets provide a means for handling files that are 1248continuously growing during the lifetime of a server. 1249Server statistics are a typical example for such files. 1250Generation file sets provide access to a set of files used 1251to store the actual data. 1252At any time at most one element 1253of the set is being written to. 1254The type given specifies 1255when and how data will be directed to a new element of the set. 1256This way, information stored in elements of a file set 1257that are currently unused are available for administrational 1258operations without the risk of disturbing the operation of ntpd. 1259(Most important: they can be removed to free space for new data 1260produced.) 1261.Pp 1262Note that this command can be sent from the 1263.Xr ntpdc @NTPDC_MS@ 1264program running at a remote location. 1265.Bl -tag -width indent 1266.It Cm name 1267This is the type of the statistics records, as shown in the 1268.Cm statistics 1269command. 1270.It Cm file Ar filename 1271This is the file name for the statistics records. 1272Filenames of set 1273members are built from three concatenated elements 1274.Ar Cm prefix , 1275.Ar Cm filename 1276and 1277.Ar Cm suffix : 1278.Bl -tag -width indent 1279.It Cm prefix 1280This is a constant filename path. 1281It is not subject to 1282modifications via the 1283.Ar filegen 1284option. 1285It is defined by the 1286server, usually specified as a compile\-time constant. 1287It may, 1288however, be configurable for individual file generation sets 1289via other commands. 1290For example, the prefix used with 1291.Ar loopstats 1292and 1293.Ar peerstats 1294generation can be configured using the 1295.Ar statsdir 1296option explained above. 1297.It Cm filename 1298This string is directly concatenated to the prefix mentioned 1299above (no intervening 1300.Ql / ) . 1301This can be modified using 1302the file argument to the 1303.Ar filegen 1304statement. 1305No 1306.Pa .. 1307elements are 1308allowed in this component to prevent filenames referring to 1309parts outside the filesystem hierarchy denoted by 1310.Ar prefix . 1311.It Cm suffix 1312This part is reflects individual elements of a file set. 1313It is 1314generated according to the type of a file set. 1315.El 1316.It Cm type Ar typename 1317A file generation set is characterized by its type. 1318The following 1319types are supported: 1320.Bl -tag -width indent 1321.It Cm none 1322The file set is actually a single plain file. 1323.It Cm pid 1324One element of file set is used per incarnation of a ntpd 1325server. 1326This type does not perform any changes to file set 1327members during runtime, however it provides an easy way of 1328separating files belonging to different 1329.Xr ntpd @NTPD_MS@ 1330server incarnations. 1331The set member filename is built by appending a 1332.Ql \&. 1333to concatenated 1334.Ar prefix 1335and 1336.Ar filename 1337strings, and 1338appending the decimal representation of the process ID of the 1339.Xr ntpd @NTPD_MS@ 1340server process. 1341.It Cm day 1342One file generation set element is created per day. 1343A day is 1344defined as the period between 00:00 and 24:00 UTC. 1345The file set 1346member suffix consists of a 1347.Ql \&. 1348and a day specification in 1349the form 1350.Cm YYYYMMdd . 1351.Cm YYYY 1352is a 4\-digit year number (e.g., 1992). 1353.Cm MM 1354is a two digit month number. 1355.Cm dd 1356is a two digit day number. 1357Thus, all information written at 10 December 1992 would end up 1358in a file named 1359.Ar prefix 1360.Ar filename Ns .19921210 . 1361.It Cm week 1362Any file set member contains data related to a certain week of 1363a year. 1364The term week is defined by computing day\-of\-year 1365modulo 7. 1366Elements of such a file generation set are 1367distinguished by appending the following suffix to the file set 1368filename base: A dot, a 4\-digit year number, the letter 1369.Cm W , 1370and a 2\-digit week number. 1371For example, information from January, 137210th 1992 would end up in a file with suffix 1373.No . Ns Ar 1992W1 . 1374.It Cm month 1375One generation file set element is generated per month. 1376The 1377file name suffix consists of a dot, a 4\-digit year number, and 1378a 2\-digit month. 1379.It Cm year 1380One generation file element is generated per year. 1381The filename 1382suffix consists of a dot and a 4 digit year number. 1383.It Cm age 1384This type of file generation sets changes to a new element of 1385the file set every 24 hours of server operation. 1386The filename 1387suffix consists of a dot, the letter 1388.Cm a , 1389and an 8\-digit number. 1390This number is taken to be the number of seconds the server is 1391running at the start of the corresponding 24\-hour period. 1392Information is only written to a file generation by specifying 1393.Cm enable ; 1394output is prevented by specifying 1395.Cm disable . 1396.El 1397.It Cm link | nolink 1398It is convenient to be able to access the current element of a file 1399generation set by a fixed name. 1400This feature is enabled by 1401specifying 1402.Cm link 1403and disabled using 1404.Cm nolink . 1405If link is specified, a 1406hard link from the current file set element to a file without 1407suffix is created. 1408When there is already a file with this name and 1409the number of links of this file is one, it is renamed appending a 1410dot, the letter 1411.Cm C , 1412and the pid of the 1413.Xr ntpd @NTPD_MS@ 1414server process. 1415When the 1416number of links is greater than one, the file is unlinked. 1417This 1418allows the current file to be accessed by a constant name. 1419.It Cm enable \&| Cm disable 1420Enables or disables the recording function. 1421.El 1422.El 1423.El 1424.Sh Access Control Support 1425The 1426.Xr ntpd @NTPD_MS@ 1427daemon implements a general purpose address/mask based restriction 1428list. 1429The list contains address/match entries sorted first 1430by increasing address values and and then by increasing mask values. 1431A match occurs when the bitwise AND of the mask and the packet 1432source address is equal to the bitwise AND of the mask and 1433address in the list. 1434The list is searched in order with the 1435last match found defining the restriction flags associated 1436with the entry. 1437Additional information and examples can be found in the 1438.Qq Notes on Configuring NTP and Setting up a NTP Subnet 1439page 1440(available as part of the HTML documentation 1441provided in 1442.Pa /usr/share/doc/ntp ) . 1443.Pp 1444The restriction facility was implemented in conformance 1445with the access policies for the original NSFnet backbone 1446time servers. 1447Later the facility was expanded to deflect 1448cryptographic and clogging attacks. 1449While this facility may 1450be useful for keeping unwanted or broken or malicious clients 1451from congesting innocent servers, it should not be considered 1452an alternative to the NTP authentication facilities. 1453Source address based restrictions are easily circumvented 1454by a determined cracker. 1455.Pp 1456Clients can be denied service because they are explicitly 1457included in the restrict list created by the 1458.Ic restrict 1459command 1460or implicitly as the result of cryptographic or rate limit 1461violations. 1462Cryptographic violations include certificate 1463or identity verification failure; rate limit violations generally 1464result from defective NTP implementations that send packets 1465at abusive rates. 1466Some violations cause denied service 1467only for the offending packet, others cause denied service 1468for a timed period and others cause the denied service for 1469an indefinite period. 1470When a client or network is denied access 1471for an indefinite period, the only way at present to remove 1472the restrictions is by restarting the server. 1473.Ss The Kiss\-of\-Death Packet 1474Ordinarily, packets denied service are simply dropped with no 1475further action except incrementing statistics counters. 1476Sometimes a 1477more proactive response is needed, such as a server message that 1478explicitly requests the client to stop sending and leave a message 1479for the system operator. 1480A special packet format has been created 1481for this purpose called the "kiss\-of\-death" (KoD) packet. 1482KoD packets have the leap bits set unsynchronized and stratum set 1483to zero and the reference identifier field set to a four\-byte 1484ASCII code. 1485If the 1486.Cm noserve 1487or 1488.Cm notrust 1489flag of the matching restrict list entry is set, 1490the code is "DENY"; if the 1491.Cm limited 1492flag is set and the rate limit 1493is exceeded, the code is "RATE". 1494Finally, if a cryptographic violation occurs, the code is "CRYP". 1495.Pp 1496A client receiving a KoD performs a set of sanity checks to 1497minimize security exposure, then updates the stratum and 1498reference identifier peer variables, sets the access 1499denied (TEST4) bit in the peer flash variable and sends 1500a message to the log. 1501As long as the TEST4 bit is set, 1502the client will send no further packets to the server. 1503The only way at present to recover from this condition is 1504to restart the protocol at both the client and server. 1505This 1506happens automatically at the client when the association times out. 1507It will happen at the server only if the server operator cooperates. 1508.Ss Access Control Commands 1509.Bl -tag -width indent 1510.It Xo Ic discard 1511.Op Cm average Ar avg 1512.Op Cm minimum Ar min 1513.Op Cm monitor Ar prob 1514.Xc 1515Set the parameters of the 1516.Cm limited 1517facility which protects the server from 1518client abuse. 1519The 1520.Cm average 1521subcommand specifies the minimum average packet 1522spacing, while the 1523.Cm minimum 1524subcommand specifies the minimum packet spacing. 1525Packets that violate these minima are discarded 1526and a kiss\-o'\-death packet returned if enabled. 1527The default 1528minimum average and minimum are 5 and 2, respectively. 1529The 1530.Ic monitor 1531subcommand specifies the probability of discard 1532for packets that overflow the rate\-control window. 1533.It Xo Ic restrict address 1534.Op Cm mask Ar mask 1535.Op Ar flag ... 1536.Xc 1537The 1538.Ar address 1539argument expressed in 1540dotted\-quad form is the address of a host or network. 1541Alternatively, the 1542.Ar address 1543argument can be a valid host DNS name. 1544The 1545.Ar mask 1546argument expressed in dotted\-quad form defaults to 1547.Cm 255.255.255.255 , 1548meaning that the 1549.Ar address 1550is treated as the address of an individual host. 1551A default entry (address 1552.Cm 0.0.0.0 , 1553mask 1554.Cm 0.0.0.0 ) 1555is always included and is always the first entry in the list. 1556Note that text string 1557.Cm default , 1558with no mask option, may 1559be used to indicate the default entry. 1560In the current implementation, 1561.Cm flag 1562always 1563restricts access, i.e., an entry with no flags indicates that free 1564access to the server is to be given. 1565The flags are not orthogonal, 1566in that more restrictive flags will often make less restrictive 1567ones redundant. 1568The flags can generally be classed into two 1569categories, those which restrict time service and those which 1570restrict informational queries and attempts to do run\-time 1571reconfiguration of the server. 1572One or more of the following flags 1573may be specified: 1574.Bl -tag -width indent 1575.It Cm ignore 1576Deny packets of all kinds, including 1577.Xr ntpq @NTPQ_MS@ 1578and 1579.Xr ntpdc @NTPDC_MS@ 1580queries. 1581.It Cm kod 1582If this flag is set when an access violation occurs, a kiss\-o'\-death 1583(KoD) packet is sent. 1584KoD packets are rate limited to no more than one 1585per second. 1586If another KoD packet occurs within one second after the 1587last one, the packet is dropped. 1588.It Cm limited 1589Deny service if the packet spacing violates the lower limits specified 1590in the 1591.Ic discard 1592command. 1593A history of clients is kept using the 1594monitoring capability of 1595.Xr ntpd @NTPD_MS@ . 1596Thus, monitoring is always active as 1597long as there is a restriction entry with the 1598.Cm limited 1599flag. 1600.It Cm lowpriotrap 1601Declare traps set by matching hosts to be low priority. 1602The 1603number of traps a server can maintain is limited (the current limit 1604is 3). 1605Traps are usually assigned on a first come, first served 1606basis, with later trap requestors being denied service. 1607This flag 1608modifies the assignment algorithm by allowing low priority traps to 1609be overridden by later requests for normal priority traps. 1610.It Cm nomodify 1611Deny 1612.Xr ntpq @NTPQ_MS@ 1613and 1614.Xr ntpdc @NTPDC_MS@ 1615queries which attempt to modify the state of the 1616server (i.e., run time reconfiguration). 1617Queries which return 1618information are permitted. 1619.It Cm noquery 1620Deny 1621.Xr ntpq @NTPQ_MS@ 1622and 1623.Xr ntpdc @NTPDC_MS@ 1624queries. 1625Time service is not affected. 1626.It Cm nopeer 1627Deny packets which would result in mobilizing a new association. 1628This 1629includes broadcast and symmetric active packets when a configured 1630association does not exist. 1631It also includes 1632.Cm pool 1633associations, so if you want to use servers from a 1634.Cm pool 1635directive and also want to use 1636.Cm nopeer 1637by default, you'll want a 1638.Cm "restrict source ..." line as well that does 1639.It not 1640include the 1641.Cm nopeer 1642directive. 1643.It Cm noserve 1644Deny all packets except 1645.Xr ntpq @NTPQ_MS@ 1646and 1647.Xr ntpdc @NTPDC_MS@ 1648queries. 1649.It Cm notrap 1650Decline to provide mode 6 control message trap service to matching 1651hosts. 1652The trap service is a subsystem of the 1653.Xr ntpq @NTPQ_MS@ 1654control message 1655protocol which is intended for use by remote event logging programs. 1656.It Cm notrust 1657Deny service unless the packet is cryptographically authenticated. 1658.It Cm ntpport 1659This is actually a match algorithm modifier, rather than a 1660restriction flag. 1661Its presence causes the restriction entry to be 1662matched only if the source port in the packet is the standard NTP 1663UDP port (123). 1664Both 1665.Cm ntpport 1666and 1667.Cm non\-ntpport 1668may 1669be specified. 1670The 1671.Cm ntpport 1672is considered more specific and 1673is sorted later in the list. 1674.It Cm version 1675Deny packets that do not match the current NTP version. 1676.El 1677.Pp 1678Default restriction list entries with the flags ignore, interface, 1679ntpport, for each of the local host's interface addresses are 1680inserted into the table at startup to prevent the server 1681from attempting to synchronize to its own time. 1682A default entry is also always present, though if it is 1683otherwise unconfigured; no flags are associated 1684with the default entry (i.e., everything besides your own 1685NTP server is unrestricted). 1686.El 1687.Sh Automatic NTP Configuration Options 1688.Ss Manycasting 1689Manycasting is a automatic discovery and configuration paradigm 1690new to NTPv4. 1691It is intended as a means for a multicast client 1692to troll the nearby network neighborhood to find cooperating 1693manycast servers, validate them using cryptographic means 1694and evaluate their time values with respect to other servers 1695that might be lurking in the vicinity. 1696The intended result is that each manycast client mobilizes 1697client associations with some number of the "best" 1698of the nearby manycast servers, yet automatically reconfigures 1699to sustain this number of servers should one or another fail. 1700.Pp 1701Note that the manycasting paradigm does not coincide 1702with the anycast paradigm described in RFC\-1546, 1703which is designed to find a single server from a clique 1704of servers providing the same service. 1705The manycast paradigm is designed to find a plurality 1706of redundant servers satisfying defined optimality criteria. 1707.Pp 1708Manycasting can be used with either symmetric key 1709or public key cryptography. 1710The public key infrastructure (PKI) 1711offers the best protection against compromised keys 1712and is generally considered stronger, at least with relatively 1713large key sizes. 1714It is implemented using the Autokey protocol and 1715the OpenSSL cryptographic library available from 1716.Li http://www.openssl.org/ . 1717The library can also be used with other NTPv4 modes 1718as well and is highly recommended, especially for broadcast modes. 1719.Pp 1720A persistent manycast client association is configured 1721using the 1722.Ic manycastclient 1723command, which is similar to the 1724.Ic server 1725command but with a multicast (IPv4 class 1726.Cm D 1727or IPv6 prefix 1728.Cm FF ) 1729group address. 1730The IANA has designated IPv4 address 224.1.1.1 1731and IPv6 address FF05::101 (site local) for NTP. 1732When more servers are needed, it broadcasts manycast 1733client messages to this address at the minimum feasible rate 1734and minimum feasible time\-to\-live (TTL) hops, depending 1735on how many servers have already been found. 1736There can be as many manycast client associations 1737as different group address, each one serving as a template 1738for a future ephemeral unicast client/server association. 1739.Pp 1740Manycast servers configured with the 1741.Ic manycastserver 1742command listen on the specified group address for manycast 1743client messages. 1744Note the distinction between manycast client, 1745which actively broadcasts messages, and manycast server, 1746which passively responds to them. 1747If a manycast server is 1748in scope of the current TTL and is itself synchronized 1749to a valid source and operating at a stratum level equal 1750to or lower than the manycast client, it replies to the 1751manycast client message with an ordinary unicast server message. 1752.Pp 1753The manycast client receiving this message mobilizes 1754an ephemeral client/server association according to the 1755matching manycast client template, but only if cryptographically 1756authenticated and the server stratum is less than or equal 1757to the client stratum. 1758Authentication is explicitly required 1759and either symmetric key or public key (Autokey) can be used. 1760Then, the client polls the server at its unicast address 1761in burst mode in order to reliably set the host clock 1762and validate the source. 1763This normally results 1764in a volley of eight client/server at 2\-s intervals 1765during which both the synchronization and cryptographic 1766protocols run concurrently. 1767Following the volley, 1768the client runs the NTP intersection and clustering 1769algorithms, which act to discard all but the "best" 1770associations according to stratum and synchronization 1771distance. 1772The surviving associations then continue 1773in ordinary client/server mode. 1774.Pp 1775The manycast client polling strategy is designed to reduce 1776as much as possible the volume of manycast client messages 1777and the effects of implosion due to near\-simultaneous 1778arrival of manycast server messages. 1779The strategy is determined by the 1780.Ic manycastclient , 1781.Ic tos 1782and 1783.Ic ttl 1784configuration commands. 1785The manycast poll interval is 1786normally eight times the system poll interval, 1787which starts out at the 1788.Cm minpoll 1789value specified in the 1790.Ic manycastclient , 1791command and, under normal circumstances, increments to the 1792.Cm maxpolll 1793value specified in this command. 1794Initially, the TTL is 1795set at the minimum hops specified by the 1796.Ic ttl 1797command. 1798At each retransmission the TTL is increased until reaching 1799the maximum hops specified by this command or a sufficient 1800number client associations have been found. 1801Further retransmissions use the same TTL. 1802.Pp 1803The quality and reliability of the suite of associations 1804discovered by the manycast client is determined by the NTP 1805mitigation algorithms and the 1806.Cm minclock 1807and 1808.Cm minsane 1809values specified in the 1810.Ic tos 1811configuration command. 1812At least 1813.Cm minsane 1814candidate servers must be available and the mitigation 1815algorithms produce at least 1816.Cm minclock 1817survivors in order to synchronize the clock. 1818Byzantine agreement principles require at least four 1819candidates in order to correctly discard a single falseticker. 1820For legacy purposes, 1821.Cm minsane 1822defaults to 1 and 1823.Cm minclock 1824defaults to 3. 1825For manycast service 1826.Cm minsane 1827should be explicitly set to 4, assuming at least that 1828number of servers are available. 1829.Pp 1830If at least 1831.Cm minclock 1832servers are found, the manycast poll interval is immediately 1833set to eight times 1834.Cm maxpoll . 1835If less than 1836.Cm minclock 1837servers are found when the TTL has reached the maximum hops, 1838the manycast poll interval is doubled. 1839For each transmission 1840after that, the poll interval is doubled again until 1841reaching the maximum of eight times 1842.Cm maxpoll . 1843Further transmissions use the same poll interval and 1844TTL values. 1845Note that while all this is going on, 1846each client/server association found is operating normally 1847it the system poll interval. 1848.Pp 1849Administratively scoped multicast boundaries are normally 1850specified by the network router configuration and, 1851in the case of IPv6, the link/site scope prefix. 1852By default, the increment for TTL hops is 32 starting 1853from 31; however, the 1854.Ic ttl 1855configuration command can be 1856used to modify the values to match the scope rules. 1857.Pp 1858It is often useful to narrow the range of acceptable 1859servers which can be found by manycast client associations. 1860Because manycast servers respond only when the client 1861stratum is equal to or greater than the server stratum, 1862primary (stratum 1) servers fill find only primary servers 1863in TTL range, which is probably the most common objective. 1864However, unless configured otherwise, all manycast clients 1865in TTL range will eventually find all primary servers 1866in TTL range, which is probably not the most common 1867objective in large networks. 1868The 1869.Ic tos 1870command can be used to modify this behavior. 1871Servers with stratum below 1872.Cm floor 1873or above 1874.Cm ceiling 1875specified in the 1876.Ic tos 1877command are strongly discouraged during the selection 1878process; however, these servers may be temporally 1879accepted if the number of servers within TTL range is 1880less than 1881.Cm minclock . 1882.Pp 1883The above actions occur for each manycast client message, 1884which repeats at the designated poll interval. 1885However, once the ephemeral client association is mobilized, 1886subsequent manycast server replies are discarded, 1887since that would result in a duplicate association. 1888If during a poll interval the number of client associations 1889falls below 1890.Cm minclock , 1891all manycast client prototype associations are reset 1892to the initial poll interval and TTL hops and operation 1893resumes from the beginning. 1894It is important to avoid 1895frequent manycast client messages, since each one requires 1896all manycast servers in TTL range to respond. 1897The result could well be an implosion, either minor or major, 1898depending on the number of servers in range. 1899The recommended value for 1900.Cm maxpoll 1901is 12 (4,096 s). 1902.Pp 1903It is possible and frequently useful to configure a host 1904as both manycast client and manycast server. 1905A number of hosts configured this way and sharing a common 1906group address will automatically organize themselves 1907in an optimum configuration based on stratum and 1908synchronization distance. 1909For example, consider an NTP 1910subnet of two primary servers and a hundred or more 1911dependent clients. 1912With two exceptions, all servers 1913and clients have identical configuration files including both 1914.Ic multicastclient 1915and 1916.Ic multicastserver 1917commands using, for instance, multicast group address 1918239.1.1.1. 1919The only exception is that each primary server 1920configuration file must include commands for the primary 1921reference source such as a GPS receiver. 1922.Pp 1923The remaining configuration files for all secondary 1924servers and clients have the same contents, except for the 1925.Ic tos 1926command, which is specific for each stratum level. 1927For stratum 1 and stratum 2 servers, that command is 1928not necessary. 1929For stratum 3 and above servers the 1930.Cm floor 1931value is set to the intended stratum number. 1932Thus, all stratum 3 configuration files are identical, 1933all stratum 4 files are identical and so forth. 1934.Pp 1935Once operations have stabilized in this scenario, 1936the primary servers will find the primary reference source 1937and each other, since they both operate at the same 1938stratum (1), but not with any secondary server or client, 1939since these operate at a higher stratum. 1940The secondary 1941servers will find the servers at the same stratum level. 1942If one of the primary servers loses its GPS receiver, 1943it will continue to operate as a client and other clients 1944will time out the corresponding association and 1945re\-associate accordingly. 1946.Pp 1947Some administrators prefer to avoid running 1948.Xr ntpd @NTPD_MS@ 1949continuously and run either 1950.Xr sntp @SNTP_MS@ 1951or 1952.Xr ntpd @NTPD_MS@ 1953.Fl q 1954as a cron job. 1955In either case the servers must be 1956configured in advance and the program fails if none are 1957available when the cron job runs. 1958A really slick 1959application of manycast is with 1960.Xr ntpd @NTPD_MS@ 1961.Fl q . 1962The program wakes up, scans the local landscape looking 1963for the usual suspects, selects the best from among 1964the rascals, sets the clock and then departs. 1965Servers do not have to be configured in advance and 1966all clients throughout the network can have the same 1967configuration file. 1968.Ss Manycast Interactions with Autokey 1969Each time a manycast client sends a client mode packet 1970to a multicast group address, all manycast servers 1971in scope generate a reply including the host name 1972and status word. 1973The manycast clients then run 1974the Autokey protocol, which collects and verifies 1975all certificates involved. 1976Following the burst interval 1977all but three survivors are cast off, 1978but the certificates remain in the local cache. 1979It often happens that several complete signing trails 1980from the client to the primary servers are collected in this way. 1981.Pp 1982About once an hour or less often if the poll interval 1983exceeds this, the client regenerates the Autokey key list. 1984This is in general transparent in client/server mode. 1985However, about once per day the server private value 1986used to generate cookies is refreshed along with all 1987manycast client associations. 1988In this case all 1989cryptographic values including certificates is refreshed. 1990If a new certificate has been generated since 1991the last refresh epoch, it will automatically revoke 1992all prior certificates that happen to be in the 1993certificate cache. 1994At the same time, the manycast 1995scheme starts all over from the beginning and 1996the expanding ring shrinks to the minimum and increments 1997from there while collecting all servers in scope. 1998.Ss Manycast Options 1999.Bl -tag -width indent 2000.It Xo Ic tos 2001.Oo 2002.Cm ceiling Ar ceiling | 2003.Cm cohort { 0 | 1 } | 2004.Cm floor Ar floor | 2005.Cm minclock Ar minclock | 2006.Cm minsane Ar minsane 2007.Oc 2008.Xc 2009This command affects the clock selection and clustering 2010algorithms. 2011It can be used to select the quality and 2012quantity of peers used to synchronize the system clock 2013and is most useful in manycast mode. 2014The variables operate 2015as follows: 2016.Bl -tag -width indent 2017.It Cm ceiling Ar ceiling 2018Peers with strata above 2019.Cm ceiling 2020will be discarded if there are at least 2021.Cm minclock 2022peers remaining. 2023This value defaults to 15, but can be changed 2024to any number from 1 to 15. 2025.It Cm cohort Bro 0 | 1 Brc 2026This is a binary flag which enables (0) or disables (1) 2027manycast server replies to manycast clients with the same 2028stratum level. 2029This is useful to reduce implosions where 2030large numbers of clients with the same stratum level 2031are present. 2032The default is to enable these replies. 2033.It Cm floor Ar floor 2034Peers with strata below 2035.Cm floor 2036will be discarded if there are at least 2037.Cm minclock 2038peers remaining. 2039This value defaults to 1, but can be changed 2040to any number from 1 to 15. 2041.It Cm minclock Ar minclock 2042The clustering algorithm repeatedly casts out outlier 2043associations until no more than 2044.Cm minclock 2045associations remain. 2046This value defaults to 3, 2047but can be changed to any number from 1 to the number of 2048configured sources. 2049.It Cm minsane Ar minsane 2050This is the minimum number of candidates available 2051to the clock selection algorithm in order to produce 2052one or more truechimers for the clustering algorithm. 2053If fewer than this number are available, the clock is 2054undisciplined and allowed to run free. 2055The default is 1 2056for legacy purposes. 2057However, according to principles of 2058Byzantine agreement, 2059.Cm minsane 2060should be at least 4 in order to detect and discard 2061a single falseticker. 2062.El 2063.It Cm ttl Ar hop ... 2064This command specifies a list of TTL values in increasing 2065order, up to 8 values can be specified. 2066In manycast mode these values are used in turn 2067in an expanding\-ring search. 2068The default is eight 2069multiples of 32 starting at 31. 2070.El 2071.Sh Reference Clock Support 2072The NTP Version 4 daemon supports some three dozen different radio, 2073satellite and modem reference clocks plus a special pseudo\-clock 2074used for backup or when no other clock source is available. 2075Detailed descriptions of individual device drivers and options can 2076be found in the 2077.Qq Reference Clock Drivers 2078page 2079(available as part of the HTML documentation 2080provided in 2081.Pa /usr/share/doc/ntp ) . 2082Additional information can be found in the pages linked 2083there, including the 2084.Qq Debugging Hints for Reference Clock Drivers 2085and 2086.Qq How To Write a Reference Clock Driver 2087pages 2088(available as part of the HTML documentation 2089provided in 2090.Pa /usr/share/doc/ntp ) . 2091In addition, support for a PPS 2092signal is available as described in the 2093.Qq Pulse\-per\-second (PPS) Signal Interfacing 2094page 2095(available as part of the HTML documentation 2096provided in 2097.Pa /usr/share/doc/ntp ) . 2098Many 2099drivers support special line discipline/streams modules which can 2100significantly improve the accuracy using the driver. 2101These are 2102described in the 2103.Qq Line Disciplines and Streams Drivers 2104page 2105(available as part of the HTML documentation 2106provided in 2107.Pa /usr/share/doc/ntp ) . 2108.Pp 2109A reference clock will generally (though not always) be a radio 2110timecode receiver which is synchronized to a source of standard 2111time such as the services offered by the NRC in Canada and NIST and 2112USNO in the US. 2113The interface between the computer and the timecode 2114receiver is device dependent, but is usually a serial port. 2115A 2116device driver specific to each reference clock must be selected and 2117compiled in the distribution; however, most common radio, satellite 2118and modem clocks are included by default. 2119Note that an attempt to 2120configure a reference clock when the driver has not been compiled 2121or the hardware port has not been appropriately configured results 2122in a scalding remark to the system log file, but is otherwise non 2123hazardous. 2124.Pp 2125For the purposes of configuration, 2126.Xr ntpd @NTPD_MS@ 2127treats 2128reference clocks in a manner analogous to normal NTP peers as much 2129as possible. 2130Reference clocks are identified by a syntactically 2131correct but invalid IP address, in order to distinguish them from 2132normal NTP peers. 2133Reference clock addresses are of the form 2134.Sm off 2135.Li 127.127. Ar t . Ar u , 2136.Sm on 2137where 2138.Ar t 2139is an integer 2140denoting the clock type and 2141.Ar u 2142indicates the unit 2143number in the range 0\-3. 2144While it may seem overkill, it is in fact 2145sometimes useful to configure multiple reference clocks of the same 2146type, in which case the unit numbers must be unique. 2147.Pp 2148The 2149.Ic server 2150command is used to configure a reference 2151clock, where the 2152.Ar address 2153argument in that command 2154is the clock address. 2155The 2156.Cm key , 2157.Cm version 2158and 2159.Cm ttl 2160options are not used for reference clock support. 2161The 2162.Cm mode 2163option is added for reference clock support, as 2164described below. 2165The 2166.Cm prefer 2167option can be useful to 2168persuade the server to cherish a reference clock with somewhat more 2169enthusiasm than other reference clocks or peers. 2170Further 2171information on this option can be found in the 2172.Qq Mitigation Rules and the prefer Keyword 2173(available as part of the HTML documentation 2174provided in 2175.Pa /usr/share/doc/ntp ) 2176page. 2177The 2178.Cm minpoll 2179and 2180.Cm maxpoll 2181options have 2182meaning only for selected clock drivers. 2183See the individual clock 2184driver document pages for additional information. 2185.Pp 2186The 2187.Ic fudge 2188command is used to provide additional 2189information for individual clock drivers and normally follows 2190immediately after the 2191.Ic server 2192command. 2193The 2194.Ar address 2195argument specifies the clock address. 2196The 2197.Cm refid 2198and 2199.Cm stratum 2200options can be used to 2201override the defaults for the device. 2202There are two optional 2203device\-dependent time offsets and four flags that can be included 2204in the 2205.Ic fudge 2206command as well. 2207.Pp 2208The stratum number of a reference clock is by default zero. 2209Since the 2210.Xr ntpd @NTPD_MS@ 2211daemon adds one to the stratum of each 2212peer, a primary server ordinarily displays an external stratum of 2213one. 2214In order to provide engineered backups, it is often useful to 2215specify the reference clock stratum as greater than zero. 2216The 2217.Cm stratum 2218option is used for this purpose. 2219Also, in cases 2220involving both a reference clock and a pulse\-per\-second (PPS) 2221discipline signal, it is useful to specify the reference clock 2222identifier as other than the default, depending on the driver. 2223The 2224.Cm refid 2225option is used for this purpose. 2226Except where noted, 2227these options apply to all clock drivers. 2228.Ss Reference Clock Commands 2229.Bl -tag -width indent 2230.It Xo Ic server 2231.Sm off 2232.Li 127.127. Ar t . Ar u 2233.Sm on 2234.Op Cm prefer 2235.Op Cm mode Ar int 2236.Op Cm minpoll Ar int 2237.Op Cm maxpoll Ar int 2238.Xc 2239This command can be used to configure reference clocks in 2240special ways. 2241The options are interpreted as follows: 2242.Bl -tag -width indent 2243.It Cm prefer 2244Marks the reference clock as preferred. 2245All other things being 2246equal, this host will be chosen for synchronization among a set of 2247correctly operating hosts. 2248See the 2249.Qq Mitigation Rules and the prefer Keyword 2250page 2251(available as part of the HTML documentation 2252provided in 2253.Pa /usr/share/doc/ntp ) 2254for further information. 2255.It Cm mode Ar int 2256Specifies a mode number which is interpreted in a 2257device\-specific fashion. 2258For instance, it selects a dialing 2259protocol in the ACTS driver and a device subtype in the 2260parse 2261drivers. 2262.It Cm minpoll Ar int 2263.It Cm maxpoll Ar int 2264These options specify the minimum and maximum polling interval 2265for reference clock messages, as a power of 2 in seconds 2266For 2267most directly connected reference clocks, both 2268.Cm minpoll 2269and 2270.Cm maxpoll 2271default to 6 (64 s). 2272For modem reference clocks, 2273.Cm minpoll 2274defaults to 10 (17.1 m) and 2275.Cm maxpoll 2276defaults to 14 (4.5 h). 2277The allowable range is 4 (16 s) to 17 (36.4 h) inclusive. 2278.El 2279.It Xo Ic fudge 2280.Sm off 2281.Li 127.127. Ar t . Ar u 2282.Sm on 2283.Op Cm time1 Ar sec 2284.Op Cm time2 Ar sec 2285.Op Cm stratum Ar int 2286.Op Cm refid Ar string 2287.Op Cm mode Ar int 2288.Op Cm flag1 Cm 0 \&| Cm 1 2289.Op Cm flag2 Cm 0 \&| Cm 1 2290.Op Cm flag3 Cm 0 \&| Cm 1 2291.Op Cm flag4 Cm 0 \&| Cm 1 2292.Xc 2293This command can be used to configure reference clocks in 2294special ways. 2295It must immediately follow the 2296.Ic server 2297command which configures the driver. 2298Note that the same capability 2299is possible at run time using the 2300.Xr ntpdc @NTPDC_MS@ 2301program. 2302The options are interpreted as 2303follows: 2304.Bl -tag -width indent 2305.It Cm time1 Ar sec 2306Specifies a constant to be added to the time offset produced by 2307the driver, a fixed\-point decimal number in seconds. 2308This is used 2309as a calibration constant to adjust the nominal time offset of a 2310particular clock to agree with an external standard, such as a 2311precision PPS signal. 2312It also provides a way to correct a 2313systematic error or bias due to serial port or operating system 2314latencies, different cable lengths or receiver internal delay. 2315The 2316specified offset is in addition to the propagation delay provided 2317by other means, such as internal DIPswitches. 2318Where a calibration 2319for an individual system and driver is available, an approximate 2320correction is noted in the driver documentation pages. 2321Note: in order to facilitate calibration when more than one 2322radio clock or PPS signal is supported, a special calibration 2323feature is available. 2324It takes the form of an argument to the 2325.Ic enable 2326command described in 2327.Sx Miscellaneous Options 2328page and operates as described in the 2329.Qq Reference Clock Drivers 2330page 2331(available as part of the HTML documentation 2332provided in 2333.Pa /usr/share/doc/ntp ) . 2334.It Cm time2 Ar secs 2335Specifies a fixed\-point decimal number in seconds, which is 2336interpreted in a driver\-dependent way. 2337See the descriptions of 2338specific drivers in the 2339.Qq Reference Clock Drivers 2340page 2341(available as part of the HTML documentation 2342provided in 2343.Pa /usr/share/doc/ntp ) . 2344.It Cm stratum Ar int 2345Specifies the stratum number assigned to the driver, an integer 2346between 0 and 15. 2347This number overrides the default stratum number 2348ordinarily assigned by the driver itself, usually zero. 2349.It Cm refid Ar string 2350Specifies an ASCII string of from one to four characters which 2351defines the reference identifier used by the driver. 2352This string 2353overrides the default identifier ordinarily assigned by the driver 2354itself. 2355.It Cm mode Ar int 2356Specifies a mode number which is interpreted in a 2357device\-specific fashion. 2358For instance, it selects a dialing 2359protocol in the ACTS driver and a device subtype in the 2360parse 2361drivers. 2362.It Cm flag1 Cm 0 \&| Cm 1 2363.It Cm flag2 Cm 0 \&| Cm 1 2364.It Cm flag3 Cm 0 \&| Cm 1 2365.It Cm flag4 Cm 0 \&| Cm 1 2366These four flags are used for customizing the clock driver. 2367The 2368interpretation of these values, and whether they are used at all, 2369is a function of the particular clock driver. 2370However, by 2371convention 2372.Cm flag4 2373is used to enable recording monitoring 2374data to the 2375.Cm clockstats 2376file configured with the 2377.Ic filegen 2378command. 2379Further information on the 2380.Ic filegen 2381command can be found in 2382.Sx Monitoring Options . 2383.El 2384.El 2385.Sh Miscellaneous Options 2386.Bl -tag -width indent 2387.It Ic broadcastdelay Ar seconds 2388The broadcast and multicast modes require a special calibration 2389to determine the network delay between the local and remote 2390servers. 2391Ordinarily, this is done automatically by the initial 2392protocol exchanges between the client and server. 2393In some cases, 2394the calibration procedure may fail due to network or server access 2395controls, for example. 2396This command specifies the default delay to 2397be used under these circumstances. 2398Typically (for Ethernet), a 2399number between 0.003 and 0.007 seconds is appropriate. 2400The default 2401when this command is not used is 0.004 seconds. 2402.It Ic calldelay Ar delay 2403This option controls the delay in seconds between the first and second 2404packets sent in burst or iburst mode to allow additional time for a modem 2405or ISDN call to complete. 2406.It Ic driftfile Ar driftfile 2407This command specifies the complete path and name of the file used to 2408record the frequency of the local clock oscillator. 2409This is the same 2410operation as the 2411.Fl f 2412command line option. 2413If the file exists, it is read at 2414startup in order to set the initial frequency and then updated once per 2415hour with the current frequency computed by the daemon. 2416If the file name is 2417specified, but the file itself does not exist, the starts with an initial 2418frequency of zero and creates the file when writing it for the first time. 2419If this command is not given, the daemon will always start with an initial 2420frequency of zero. 2421.Pp 2422The file format consists of a single line containing a single 2423floating point number, which records the frequency offset measured 2424in parts\-per\-million (PPM). 2425The file is updated by first writing 2426the current drift value into a temporary file and then renaming 2427this file to replace the old version. 2428This implies that 2429.Xr ntpd @NTPD_MS@ 2430must have write permission for the directory the 2431drift file is located in, and that file system links, symbolic or 2432otherwise, should be avoided. 2433.It Ic dscp Ar value 2434This option specifies the Differentiated Services Control Point (DSCP) value, 2435a 6\-bit code. 2436The default value is 46, signifying Expedited Forwarding. 2437.It Xo Ic enable 2438.Oo 2439.Cm auth | Cm bclient | 2440.Cm calibrate | Cm kernel | 2441.Cm mode7 | Cm monitor | 2442.Cm ntp | Cm stats | 2443.Cm unpeer_crypto_early | Cm unpeer_crypto_nak_early | Cm unpeer_digest_early 2444.Oc 2445.Xc 2446.It Xo Ic disable 2447.Oo 2448.Cm auth | Cm bclient | 2449.Cm calibrate | Cm kernel | 2450.Cm mode7 | Cm monitor | 2451.Cm ntp | Cm stats | 2452.Cm unpeer_crypto_early | Cm unpeer_crypto_nak_early | Cm unpeer_digest_early 2453.Oc 2454.Xc 2455Provides a way to enable or disable various server options. 2456Flags not mentioned are unaffected. 2457Note that all of these flags 2458can be controlled remotely using the 2459.Xr ntpdc @NTPDC_MS@ 2460utility program. 2461.Bl -tag -width indent 2462.It Cm auth 2463Enables the server to synchronize with unconfigured peers only if the 2464peer has been correctly authenticated using either public key or 2465private key cryptography. 2466The default for this flag is 2467.Ic enable . 2468.It Cm bclient 2469Enables the server to listen for a message from a broadcast or 2470multicast server, as in the 2471.Ic multicastclient 2472command with default 2473address. 2474The default for this flag is 2475.Ic disable . 2476.It Cm calibrate 2477Enables the calibrate feature for reference clocks. 2478The default for 2479this flag is 2480.Ic disable . 2481.It Cm kernel 2482Enables the kernel time discipline, if available. 2483The default for this 2484flag is 2485.Ic enable 2486if support is available, otherwise 2487.Ic disable . 2488.It Cm mode7 2489Enables processing of NTP mode 7 implementation\-specific requests 2490which are used by the deprecated 2491.Xr ntpdc @NTPDC_MS@ 2492program. 2493The default for this flag is disable. 2494This flag is excluded from runtime configuration using 2495.Xr ntpq @NTPQ_MS@ . 2496The 2497.Xr ntpq @NTPQ_MS@ 2498program provides the same capabilities as 2499.Xr ntpdc @NTPDC_MS@ 2500using standard mode 6 requests. 2501.It Cm monitor 2502Enables the monitoring facility. 2503See the 2504.Xr ntpdc @NTPDC_MS@ 2505program 2506and the 2507.Ic monlist 2508command or further information. 2509The 2510default for this flag is 2511.Ic enable . 2512.It Cm ntp 2513Enables time and frequency discipline. 2514In effect, this switch opens and 2515closes the feedback loop, which is useful for testing. 2516The default for 2517this flag is 2518.Ic enable . 2519.It Cm stats 2520Enables the statistics facility. 2521See the 2522.Sx Monitoring Options 2523section for further information. 2524The default for this flag is 2525.Ic disable . 2526.It Cm unpeer_crypto_early 2527By default, if 2528.Xr ntpd @NTPD_MS@ 2529receives an autokey packet that fails TEST9, 2530a crypto failure, 2531the association is immediately cleared. 2532This is almost certainly a feature, 2533but if, in spite of the current recommendation of not using autokey, 2534you are 2535.B still 2536using autokey 2537.B and 2538you are seeing this sort of DoS attack 2539disabling this flag will delay 2540tearing down the association until the reachability counter 2541becomes zero. 2542You can check your 2543.Cm peerstats 2544file for evidence of any of these attacks. 2545The 2546default for this flag is 2547.Ic enable . 2548.It Cm unpeer_crypto_nak_early 2549By default, if 2550.Xr ntpd @NTPD_MS@ 2551receives a crypto\-NAK packet that 2552passes the duplicate packet and origin timestamp checks 2553the association is immediately cleared. 2554While this is generally a feature 2555as it allows for quick recovery if a server key has changed, 2556a properly forged and appropriately delivered crypto\-NAK packet 2557can be used in a DoS attack. 2558If you have active noticable problems with this type of DoS attack 2559then you should consider 2560disabling this option. 2561You can check your 2562.Cm peerstats 2563file for evidence of any of these attacks. 2564The 2565default for this flag is 2566.Ic enable . 2567.It Cm unpeer_digest_early 2568By default, if 2569.Xr ntpd @NTPD_MS@ 2570receives what should be an authenticated packet 2571that passes other packet sanity checks but 2572contains an invalid digest 2573the association is immediately cleared. 2574While this is generally a feature 2575as it allows for quick recovery, 2576if this type of packet is carefully forged and sent 2577during an appropriate window it can be used for a DoS attack. 2578If you have active noticable problems with this type of DoS attack 2579then you should consider 2580disabling this option. 2581You can check your 2582.Cm peerstats 2583file for evidence of any of these attacks. 2584The 2585default for this flag is 2586.Ic enable . 2587.El 2588.It Ic includefile Ar includefile 2589This command allows additional configuration commands 2590to be included from a separate file. 2591Include files may 2592be nested to a depth of five; upon reaching the end of any 2593include file, command processing resumes in the previous 2594configuration file. 2595This option is useful for sites that run 2596.Xr ntpd @NTPD_MS@ 2597on multiple hosts, with (mostly) common options (e.g., a 2598restriction list). 2599.It Ic leapsmearinterval Ar seconds 2600This EXPERIMENTAL option is only available if 2601.Xr ntpd @NTPD_MS@ 2602was built with the 2603.Cm \-\-enable\-leap\-smear 2604option to the 2605.Cm configure 2606script. 2607It specifies the interval over which a leap second correction will be applied. 2608Recommended values for this option are between 26097200 (2 hours) and 86400 (24 hours). 2610.Sy DO NOT USE THIS OPTION ON PUBLIC\-ACCESS SERVERS! 2611See http://bugs.ntp.org/2855 for more information. 2612.It Ic logconfig Ar configkeyword 2613This command controls the amount and type of output written to 2614the system 2615.Xr syslog 3 2616facility or the alternate 2617.Ic logfile 2618log file. 2619By default, all output is turned on. 2620All 2621.Ar configkeyword 2622keywords can be prefixed with 2623.Ql = , 2624.Ql + 2625and 2626.Ql \- , 2627where 2628.Ql = 2629sets the 2630.Xr syslog 3 2631priority mask, 2632.Ql + 2633adds and 2634.Ql \- 2635removes 2636messages. 2637.Xr syslog 3 2638messages can be controlled in four 2639classes 2640.Po 2641.Cm clock , 2642.Cm peer , 2643.Cm sys 2644and 2645.Cm sync 2646.Pc . 2647Within these classes four types of messages can be 2648controlled: informational messages 2649.Po 2650.Cm info 2651.Pc , 2652event messages 2653.Po 2654.Cm events 2655.Pc , 2656statistics messages 2657.Po 2658.Cm statistics 2659.Pc 2660and 2661status messages 2662.Po 2663.Cm status 2664.Pc . 2665.Pp 2666Configuration keywords are formed by concatenating the message class with 2667the event class. 2668The 2669.Cm all 2670prefix can be used instead of a message class. 2671A 2672message class may also be followed by the 2673.Cm all 2674keyword to enable/disable all 2675messages of the respective message class. 2676Thus, a minimal log configuration 2677could look like this: 2678.Bd -literal 2679logconfig =syncstatus +sysevents 2680.Ed 2681.Pp 2682This would just list the synchronizations state of 2683.Xr ntpd @NTPD_MS@ 2684and the major system events. 2685For a simple reference server, the 2686following minimum message configuration could be useful: 2687.Bd -literal 2688logconfig =syncall +clockall 2689.Ed 2690.Pp 2691This configuration will list all clock information and 2692synchronization information. 2693All other events and messages about 2694peers, system events and so on is suppressed. 2695.It Ic logfile Ar logfile 2696This command specifies the location of an alternate log file to 2697be used instead of the default system 2698.Xr syslog 3 2699facility. 2700This is the same operation as the 2701.Fl l 2702command line option. 2703.It Ic setvar Ar variable Op Cm default 2704This command adds an additional system variable. 2705These 2706variables can be used to distribute additional information such as 2707the access policy. 2708If the variable of the form 2709.Sm off 2710.Va name = Ar value 2711.Sm on 2712is followed by the 2713.Cm default 2714keyword, the 2715variable will be listed as part of the default system variables 2716.Po 2717.Xr ntpq @NTPQ_MS@ 2718.Ic rv 2719command 2720.Pc ) . 2721These additional variables serve 2722informational purposes only. 2723They are not related to the protocol 2724other that they can be listed. 2725The known protocol variables will 2726always override any variables defined via the 2727.Ic setvar 2728mechanism. 2729There are three special variables that contain the names 2730of all variable of the same group. 2731The 2732.Va sys_var_list 2733holds 2734the names of all system variables. 2735The 2736.Va peer_var_list 2737holds 2738the names of all peer variables and the 2739.Va clock_var_list 2740holds the names of the reference clock variables. 2741.It Xo Ic tinker 2742.Oo 2743.Cm allan Ar allan | 2744.Cm dispersion Ar dispersion | 2745.Cm freq Ar freq | 2746.Cm huffpuff Ar huffpuff | 2747.Cm panic Ar panic | 2748.Cm step Ar step | 2749.Cm stepback Ar stepback | 2750.Cm stepfwd Ar stepfwd | 2751.Cm stepout Ar stepout 2752.Oc 2753.Xc 2754This command can be used to alter several system variables in 2755very exceptional circumstances. 2756It should occur in the 2757configuration file before any other configuration options. 2758The 2759default values of these variables have been carefully optimized for 2760a wide range of network speeds and reliability expectations. 2761In 2762general, they interact in intricate ways that are hard to predict 2763and some combinations can result in some very nasty behavior. 2764Very 2765rarely is it necessary to change the default values; but, some 2766folks cannot resist twisting the knobs anyway and this command is 2767for them. 2768Emphasis added: twisters are on their own and can expect 2769no help from the support group. 2770.Pp 2771The variables operate as follows: 2772.Bl -tag -width indent 2773.It Cm allan Ar allan 2774The argument becomes the new value for the minimum Allan 2775intercept, which is a parameter of the PLL/FLL clock discipline 2776algorithm. 2777The value in log2 seconds defaults to 7 (1024 s), which is also the lower 2778limit. 2779.It Cm dispersion Ar dispersion 2780The argument becomes the new value for the dispersion increase rate, 2781normally .000015 s/s. 2782.It Cm freq Ar freq 2783The argument becomes the initial value of the frequency offset in 2784parts\-per\-million. 2785This overrides the value in the frequency file, if 2786present, and avoids the initial training state if it is not. 2787.It Cm huffpuff Ar huffpuff 2788The argument becomes the new value for the experimental 2789huff\-n'\-puff filter span, which determines the most recent interval 2790the algorithm will search for a minimum delay. 2791The lower limit is 2792900 s (15 m), but a more reasonable value is 7200 (2 hours). 2793There 2794is no default, since the filter is not enabled unless this command 2795is given. 2796.It Cm panic Ar panic 2797The argument is the panic threshold, normally 1000 s. 2798If set to zero, 2799the panic sanity check is disabled and a clock offset of any value will 2800be accepted. 2801.It Cm step Ar step 2802The argument is the step threshold, which by default is 0.128 s. 2803It can 2804be set to any positive number in seconds. 2805If set to zero, step 2806adjustments will never occur. 2807Note: The kernel time discipline is 2808disabled if the step threshold is set to zero or greater than the 2809default. 2810.It Cm stepback Ar stepback 2811The argument is the step threshold for the backward direction, 2812which by default is 0.128 s. 2813It can 2814be set to any positive number in seconds. 2815If both the forward and backward step thresholds are set to zero, step 2816adjustments will never occur. 2817Note: The kernel time discipline is 2818disabled if 2819each direction of step threshold are either 2820set to zero or greater than .5 second. 2821.It Cm stepfwd Ar stepfwd 2822As for stepback, but for the forward direction. 2823.It Cm stepout Ar stepout 2824The argument is the stepout timeout, which by default is 900 s. 2825It can 2826be set to any positive number in seconds. 2827If set to zero, the stepout 2828pulses will not be suppressed. 2829.El 2830.It Xo Ic rlimit 2831.Oo 2832.Cm memlock Ar Nmegabytes | 2833.Cm stacksize Ar N4kPages 2834.Cm filenum Ar Nfiledescriptors 2835.Oc 2836.Xc 2837.Bl -tag -width indent 2838.It Cm memlock Ar Nmegabytes 2839Specify the number of megabytes of memory that should be 2840allocated and locked. 2841Probably only available under Linux, this option may be useful 2842when dropping root (the 2843.Fl i 2844option). 2845The default is 32 megabytes on non\-Linux machines, and \-1 under Linux. 2846-1 means "do not lock the process into memory". 28470 means "lock whatever memory the process wants into memory". 2848.It Cm stacksize Ar N4kPages 2849Specifies the maximum size of the process stack on systems with the 2850.Fn mlockall 2851function. 2852Defaults to 50 4k pages (200 4k pages in OpenBSD). 2853.It Cm filenum Ar Nfiledescriptors 2854Specifies the maximum number of file descriptors ntpd may have open at once. 2855Defaults to the system default. 2856.El 2857.It Xo Ic trap Ar host_address 2858.Op Cm port Ar port_number 2859.Op Cm interface Ar interface_address 2860.Xc 2861This command configures a trap receiver at the given host 2862address and port number for sending messages with the specified 2863local interface address. 2864If the port number is unspecified, a value 2865of 18447 is used. 2866If the interface address is not specified, the 2867message is sent with a source address of the local interface the 2868message is sent through. 2869Note that on a multihomed host the 2870interface used may vary from time to time with routing changes. 2871.Pp 2872The trap receiver will generally log event messages and other 2873information from the server in a log file. 2874While such monitor 2875programs may also request their own trap dynamically, configuring a 2876trap receiver will ensure that no messages are lost when the server 2877is started. 2878.It Cm hop Ar ... 2879This command specifies a list of TTL values in increasing order, up to 8 2880values can be specified. 2881In manycast mode these values are used in turn in 2882an expanding\-ring search. 2883The default is eight multiples of 32 starting at 288431. 2885.El 2886.Sh "OPTIONS" 2887.Bl -tag 2888.It Fl \-help 2889Display usage information and exit. 2890.It Fl \-more\-help 2891Pass the extended usage information through a pager. 2892.It Fl \-version Op Brq Ar v|c|n 2893Output version of program and exit. The default mode is `v', a simple 2894version. The `c' mode will print copyright information and `n' will 2895print the full copyright notice. 2896.El 2897.Sh "OPTION PRESETS" 2898Any option that is not marked as \fInot presettable\fP may be preset 2899by loading values from environment variables named: 2900.nf 2901 \fBNTP_CONF_<option\-name>\fP or \fBNTP_CONF\fP 2902.fi 2903.ad 2904.Sh "ENVIRONMENT" 2905See \fBOPTION PRESETS\fP for configuration environment variables. 2906.Sh FILES 2907.Bl -tag -width /etc/ntp.drift -compact 2908.It Pa /etc/ntp.conf 2909the default name of the configuration file 2910.It Pa ntp.keys 2911private MD5 keys 2912.It Pa ntpkey 2913RSA private key 2914.It Pa ntpkey_ Ns Ar host 2915RSA public key 2916.It Pa ntp_dh 2917Diffie\-Hellman agreement parameters 2918.El 2919.Sh "EXIT STATUS" 2920One of the following exit values will be returned: 2921.Bl -tag 2922.It 0 " (EXIT_SUCCESS)" 2923Successful program execution. 2924.It 1 " (EXIT_FAILURE)" 2925The operation failed or the command syntax was not valid. 2926.It 70 " (EX_SOFTWARE)" 2927libopts had an internal operational error. Please report 2928it to autogen\-users@lists.sourceforge.net. Thank you. 2929.El 2930.Sh "SEE ALSO" 2931.Xr ntpd @NTPD_MS@ , 2932.Xr ntpdc @NTPDC_MS@ , 2933.Xr ntpq @NTPQ_MS@ 2934.Pp 2935In addition to the manual pages provided, 2936comprehensive documentation is available on the world wide web 2937at 2938.Li http://www.ntp.org/ . 2939A snapshot of this documentation is available in HTML format in 2940.Pa /usr/share/doc/ntp . 2941.Rs 2942.%A David L. Mills 2943.%T Network Time Protocol (Version 4) 2944.%O RFC5905 2945.Re 2946.Sh "AUTHORS" 2947The University of Delaware and Network Time Foundation 2948.Sh "COPYRIGHT" 2949Copyright (C) 1992\-2016 The University of Delaware and Network Time Foundation all rights reserved. 2950This program is released under the terms of the NTP license, <http://ntp.org/license>. 2951.Sh BUGS 2952The syntax checking is not picky; some combinations of 2953ridiculous and even hilarious options and modes may not be 2954detected. 2955.Pp 2956The 2957.Pa ntpkey_ Ns Ar host 2958files are really digital 2959certificates. 2960These should be obtained via secure directory 2961services when they become universally available. 2962.Pp 2963Please send bug reports to: http://bugs.ntp.org, bugs@ntp.org 2964.Sh NOTES 2965This document was derived from FreeBSD. 2966.Pp 2967This manual page was \fIAutoGen\fP\-erated from the \fBntp.conf\fP 2968option definitions. 2969